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Need help with Prime number Loop and with boolean statement

Kwasi Roberts
Greenhorn

Joined: May 28, 2011
Posts: 4
Can someone tell me where I'm going wrong here in making this read all prime numbers
import java.util.*;

Here is my original code


Here is the code where I was asked to combine a while loop with a boolean statement. I need help on both.



[Edit: put code between [code] and [/code] ubb code blocks]
Andrew Monkhouse
author and jackaroo
Marshal Commander

Joined: Mar 28, 2003
Posts: 11460
    
  94

For the first class:
  • What is the definition of a Prime number? How are you handling the two conditions to validate that it is a prime?
  • What are you trying to do in lines 20 - 22?


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    Campbell Ritchie
    Sheriff

    Joined: Oct 13, 2005
    Posts: 38881
        
      23
    You are both mistaken using ½ the number as the limit for testing whether it is prime. You ought to use √number. You also should use a Sieve of Eratosthenes to populate a boolean array and that will tell you whether a number is prime or not. Much faster and efficient than using the % operator. If you look in the Wikipedia article which appears from that link, there is the Sieve of Euler, too.
    Andrew Monkhouse
    author and jackaroo
    Marshal Commander

    Joined: Mar 28, 2003
    Posts: 11460
        
      94

    vinayak jog - thank you for replying, however at CodeRanch we work on the theory that we want to teach people how to solve the problems themselves. Complete solutions don't lend themselves to that - the learning experience is removed.

    I therefore removed your response.
     
    Consider Paul's rocket mass heater.
     
    subject: Need help with Prime number Loop and with boolean statement